The invention relates to a DC overcurrent protection apparatus, which comprises an ignition current-controlled irreversible high-current switch-off element, an overcurrent detection unit and control contacts for controlling the ignition current-controlled irreversible high-current switch-off element.
Many applications exist in which a direct current, also described as a DC current, must be restricted to a maximum value, in order to protect components against an overcurrent in the event of an overload or a short-circuit. One example is the high-voltage on-board network of an electric or hybrid vehicle. In this example, two contactors and a fuse are customarily incorporated in a high-voltage battery. The contactors isolate the high-voltage battery from other components in the vehicle in normal duty, and in the event of smaller overload currents. The fuse assumes the isolating function in the event of high overload and short-circuit currents. A conventional fuse has a disadvantage, in that it operates by the thermal principle, and thus requires a long current-dependent time interval for the interruption of the current flow. Accordingly, in the event of not too high currents, it may not be sufficiently rapid to protect the vehicle components against an overload.
In consequence, concepts already exist in which a pyrotechnic switch-off element is employed, in addition to conventional switching elements (contactors, fuses). An ignition element (also described as a detonator) of the pyrotechnic switch-off element is tripped by means of a current signal, and executes the interruption of the high-current path. The ignition signal is generated by an electronic control circuit, which measures the high current to be monitored and generates the ignition signal immediately the current in the high-voltage network exceeds a maximum permissible value.
This type of actuation of the pyrotechnic switch-off element has the following disadvantages: the current measurement circuit can be disturbed, and this disturbance can result in spurious tripping or, conversely, in non-tripping in response to an overcurrent. The current measurement circuit incorporating ignition electronics can be of a complex design, with a high failure rate. For its operation, the current measurement circuit requires energy at all times, and thus increases current consumption, if it is not completely deactivated.
The object of the present invention is the alleviation or elimination of the above-mentioned disadvantages of the prior art. Specifically, a DC overcurrent protection apparatus is disclosed which, for the prevention of spurious tripping, is insensitive to disturbances, specifically electromagnetic disturbances, is not associated with continuous current consumption, has a low failure rate, and responds rapidly to an overcurrent.
According to the invention, the above-mentioned object is fulfilled by the characteristics of the independent claim. Advantageous embodiments are the subject matter of sub-claims.
The DC overcurrent protection apparatus according to the invention comprises an ignition current-controlled irreversible high-current switch-off element, an overcurrent detection unit which is electrically connected in a high-current path in series with the ignition current-controlled irreversible high-current switch-off element, and control contacts for controlling the ignition current-controlled irreversible high-current switch-off element, which are arranged such that they can be electrically connected to one another. The overcurrent detection unit is designed such that, when an overcurrent with a value equal to or greater than a predetermined current value flows in the high-current path, the control contacts, on account of an electromagnetic force which is generated by the overcurrent, are electrically connected to each other in such a way that an ignition current is transmitted to the ignition current-controlled irreversible high-current switch-off element, so that the ignition current-controlled irreversible high-current switch-off element is switched by control to a switched-off state.
In one form of embodiment of the invention, the ignition current-controlled irreversible high-current switch-off element is a pyrotechnic switch-off element. Hereinafter, a normal current is understood as a current having a value in the range of approximately 1,000 amperes (abbreviated hereinafter to “A”) to approximately 1,500 A. Currents equal to or greater than approximately 1,500 A and smaller than approximately 3,000 A can be reversibly switched by means of a contactor. The high-current path is understood as an electrical path which conducts high currents equal to or greater than approximately 1,500 A up to a value of less than approximately 3,000 A. In one form of embodiment, currents of this type can be present in a high-voltage on-board network, which carries voltages between approximately 400 V and approximately 800 V, in a vehicle, specifically an electric, hybrid or fuel cell vehicle. Beyond approximately 3,000 A, an overcurrent may be present such that, in one form of embodiment, the predefined current value in the high-current path is approximately 3,000 A, and specifically is 3,000 A.
The electromagnetic force generated by the overcurrent can be, for example, a Lorentz force. The electromagnetic force is also understood as the force which, upon the flow of an electric current in any contact arrangement in the high-current path, is such that at least partially opposing and mutually touching high-current contact elements in said contact arrangement are mutually repulsed by the flow of current. This repulsive force occurs if the current in one of the two contact elements flows in one direction, transversely to a contact surface of said contact element and, in the other of the two contact elements, flows in another direction, transversely to a contact surface of the other contact element. The partially or totally mutually opposing, but at least directionally differing partial currents of the current flowing in the contact arrangement generate a repulsive force on the contact surfaces of the high-current contact elements of said contact arrangement. This effect in DC contacts is also described as electromagnetic levitation.
The apparatus according to the invention is insensitive to disturbances, specifically to electromagnetic disturbances which can impair a current measurement, but do not have sufficient energy to generate an electromagnetic force of sufficient magnitude and duration to cause the mutual electrical bonding of the control contacts. Spurious tripping of the irreversible high-current switch-off element by electromagnetic disturbances of this type is prevented accordingly.
In response to an electromagnetic force generated by the overcurrent, the control contacts which, at a high current which lies below the overcurrent value, are mutually separated, i.e. open, are mutually bonded, i.e. short-circuited, or are connected to an energy source for the generation of the ignition current, in order to transmit the ignition current to the ignition current-controlled irreversible high-current switch-off element. Accordingly, the electrical energy required to initiate the transmission of the ignition current is only tapped from the high-current path if an overcurrent is present. The apparatus according to the invention thus features no continuous current consumption. Forms of embodiment, described with reference to the figures hereinafter, for the generation of the electromagnetic force, associated with the overcurrent, for the mutual electrical connection of the control contacts can be realized without the use of electronic components, such that the failure rate of the apparatus is very low, and is reduced in comparison with conventional apparatuses. As a result of the simple design of the apparatus according to the invention, which employs the overcurrent for the transmission of the ignition current to the irreversible high-current switch-off element, the apparatus responds very rapidly, and more rapidly than conventional apparatuses.
In one form of embodiment of the invention, the overcurrent detection unit incorporates a retaining element, which is arranged between a wall section of the overcurrent detection unit and a permanent magnet which is moveable in relation to said wall section and held in the direction of the wall section by a retaining force of the retaining element, and to which a first control contact is attached. The high-current path is configured as a winding around the permanent magnet, and the overcurrent detection unit is configured such that, if the overcurrent flows in the high-current path, the permanent magnet moves against the retaining force of the retaining element, such that the first control contact engages with a second stationary control contact, which is arranged opposite said wall section. As a result, the first control contact is short-circuited with the second control contact, such that an energy source which is connected to the second control contact transmits the ignition current to the ignition current-controlled irreversible high-current switch-off element.
The arrangement for the short-circuiting of the control contacts is of simple conception, and comprises only a high-current path winding, the permanent magnet and a retaining element. Consequently, this DC overcurrent protection apparatus according to the invention is exceptionally fail-safe and reliable, and trips rapidly in the event of an overcurrent. Energy is only tapped from the high-current path in the event of an overcurrent, as a result of which the apparatus consumes little current. In this form of embodiment, the overcurrent detection unit is completely reversible, i.e. it can be reused, with no modification, further to the occurrence of an overcurrent, and is therefore reliable and of a low-maintenance design.
Only the spontaneous discharging of the energy source for the generation of the ignition current will require compensation on an occasional basis. A capacitor, a double-layer capacitor, a battery, a high-voltage battery supplying the on-board network which is to be protected against an overcurrent itself, or similar, can be employed as an energy source. Where applicable, a charging circuit can be implemented which recharges the energy source periodically, or in the event of a decline to a minimum energy value which is required for the maintenance of the operation of the energy source, in order to offset spontaneous discharging.
In this form of embodiment, the control contacts are incorporated in the overcurrent detection unit. However, forms of embodiment are also conceivable in which the permanent magnet is brought out of a housing of the overcurrent detection unit, and the first and/or second control contact are/is arranged outside the overcurrent detection unit.
The winding can be configured such that the high-current path incorporates an inductance, which comprises at least one loop.
In a further form of embodiment of the invention, the overcurrent detection unit incorporates a retaining element, which is arranged between a wall section of the overcurrent detection unit and a high-current-conducting bracket, which is moveable in relation to said wall section, to which a first control contact is attached. The bracket is held in the direction of the wall section by a retaining force of the retaining element, such that a flow of current in the high-current path is routed through the bracket, and the bracket constitutes an element of the high-current path. The overcurrent detection unit is configured such that, if the overcurrent flows in the high-current path, the bracket moves against the retaining force of the retaining element, such that the first control contact engages with a second stationary control contact, which is arranged opposite said wall section, as a result of which the first control contact is short-circuited with the second control contact. By means of this short-circuit, an energy source which is connected to the second control contact transmits the ignition current to the ignition current-controlled irreversible high-current switch-off element.
The first control contact can be separated from the bracket by an insulating element in the form of an insulating layer. The insulating element can be formed of plastic, or of another non-conductive material. The first control contact can be fitted to one side of the bracket, which is arranged opposite a side of the bracket to which the retaining element is attached.
As the bracket constitutes an element of the high-current path, the design of the short-circuiting arrangement for the control contacts can be even simpler than in the preceding forms of embodiment, and require only the incorporation of two contact points in the high-current path for the constitution of the bracket, and the fitting of a retaining element to the bracket. In this form of embodiment, the control contacts are incorporated in the overcurrent detection unit. In other forms of embodiment, the first and/or the second control contact can be arranged outside the overcurrent detection unit.
In a particular form of embodiment of the invention, the overcurrent detection unit incorporates a retaining element, which is arranged between a wall section of the overcurrent detection unit and a high-current-conducting bracket, which is moveable in relation to said wall section. The bracket is retained by a retaining force of the retaining element in the direction of the wall section, such that a current flow in the high-current path is routed through the bracket, and the bracket constitutes an element of the high-current path. In one direction of the current flow in the high-current path, a first control contact, up-circuit of the element of the high-current path constituted by the bracket, and a second control contact, down-circuit of the element of the high-current path constituted by the bracket, are respectively connected to the high-current path. The overcurrent detection unit is configured such that, if the overcurrent flows in the high-current path, the bracket, against the retaining force of the retaining element, moves away from the element of the high-current path which is not constituted by the bracket such that, on at least one high-current contact point between the bracket and the element of the high-current path which is not constituted by the bracket, an arc is generated, the resistance of which results in a voltage drop across the first and second control contacts. In response to the voltage and the resistance, the ignition current is transmitted to the ignition current-controlled irreversible high-current switch-off element.
In this form of embodiment, the arc which is generated when the bracket, in the event of an overcurrent, is separated from that element of the high-current path which is not constituted by the bracket, is employed as an energy source for the generation of the ignition current. An arc can occur at either end of the bracket. Alternatively, one end of the bracket can be rotatable, and connected to that element of the high-current path which is not constituted by the bracket in an electrically conductive manner. Conversely to the forms of embodiment described above, the control contacts are therefore not short-circuited, but are electrically interconnected via a resistance, which is constituted by the arc. The control contacts which are connected to that element of the high-current path which is not constituted by the bracket can be arranged such that the bracket is connected in-circuit between the control contacts. Accordingly, an arrangement of the control contacts, or of one of the two control contacts, either within or outside the overcurrent detection unit is possible.
In the forms of embodiment of the invention with the bracket described, the retaining element can be configured as a solid retainer, which fails if the electromagnetic force generated by the overcurrent exceeds a predefined value. The retaining element can thus be constituted in a simple and cost-effective manner.
In a further form of embodiment of the DC overcurrent protection apparatus according to the invention, the overcurrent detection unit incorporates a retaining element, which is arranged between a wall section of the overcurrent detection unit and a high-current-conducting bracket, which is moveable in relation to said wall section. The bracket is retained by a retaining force of the retaining element in the direction of the wall section, and a permanent magnet is attached to the bracket and is carried in a winding such that, if no control voltage from a voltage source is present on the winding, a flow of current in the high-current path through the bracket is prevented, and the bracket does not constitute an element of the high-current path. If the control voltage from the voltage source is present on the winding, and a current which is smaller than the predefined current is flowing in the high-current path, the bracket moves against the retaining force of the retaining element, such that the flow of current in the high-current path is routed through the bracket, and the bracket constitutes an element of the high-current path. In one direction of the current flow in the high-current path, a first control contact, up-circuit of the element of the high-current path constituted by the bracket, and a second control contact, down-circuit of the element of the high-current path constituted by the bracket, are respectively connected to the high-current path. Between at least one of the first and second control contacts and the ignition current-controlled irreversible high-current switch-off element, a contactor, which is connected to the voltage source, is connected in-circuit such that, if no control voltage from the voltage source is present on the winding and on the contactor, and the bracket does not constitute an element of the high-current path, a no-load voltage which is present across the first and second control contacts does not result in the transmission of the ignition current to the ignition current-controlled irreversible high-current switch-off element. The overcurrent detection unit is configured such that, if the overcurrent flows in the high-current path, the bracket, notwithstanding the control voltage from the voltage source which is present on the winding and on the contactor, moves away from that element of the high-current path which is not constituted by the bracket, in the direction of the retaining force of the retaining element, such that, on at least one high-current contact point between the bracket and the element of the high-current path which is not constituted by the bracket, an arc is generated. The arc has a resistance, which results in a voltage drop across the first and second control contacts. In response to the voltage and the resistance, the ignition current is transmitted to the ignition current-controlled irreversible high-current switch-off element.
In this form of embodiment, the overcurrent detection unit constitutes a high-voltage contactor, wherein, by means of the contactor, it is prevented that any no-load voltage which is present across the bracket when the high-voltage contactor is open results in the transmission of the ignition current to the irreversible high-current switch-off element. Consequently, this switch-off element is only tripped if the high-voltage contactor is closed to permit a flow of current in the high-current path, and an overcurrent occurs such that an arc is generated between the bracket and the element of the high-current path which is not constituted by the bracket which is sufficient to trip the interruption by the irreversible high-current switch-off element of the current flow in the high-current path. At currents below the overcurrent, or in the event of a residual current flow, the overcurrent detection unit can reversibly interrupt or close the high-current path.
Advantageously, in all the DC overcurrent protection apparatuses according to the invention described above, the retaining element can be configured as a spring.
The DC overcurrent protection apparatus according to the invention, in an advantageous form of embodiment, can be incorporated in a housing and/or in the form of a subassembly.
The DC overcurrent protection apparatus according to the invention can additionally be incorporated in a high-voltage on-board network of a vehicle, preferably of an electric or hybrid vehicle.
Exemplary embodiments of the invention are described in greater detail hereinafter with reference to figures. In the interests of clarity, any true-to-scale or proportionally accurate representation has been omitted from the figures. In the figures, unless indicated otherwise, the same reference symbols identify identical components, having the same significance.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.